Deposit locks of this type are known from DE-A-25 54 916 (British Patent specification 1 564 328) and have since been out on the market in different constructional forms. Since the release of the cart is possible only by inserting a coin in the deposit lock, and the coin can only be retrieved by the user when the cart has been recoupled at one of the various collection sites, the carts no longer stand around uselessly. Because the carts not in use would always be available at the points where needed and are no longer uselessly scattered about the area, there is a saving of personnel to look for, collect and return carts to the collection sites, and one manages with a smaller number of carts.
At the moment, deposit locks are constructed in such a way that they can be operated with 1 mark or 2 mark coins or with respective foreign currency of similar value, so that the user has sufficient incentive to return the cart to one of the collection sites after use.
Quite recently, plastic chips corresponding in size to the respective deposit coins are being offered as substitutes for the above-mentioned deposit coins and in their place permit activation of the deposit lock. At this time, these plastic chips are still being widely offered at the price of the coins for which they substitute. However, the production cost of the plastic chips is only on the order of a few cents. One must therefore take into account that these chips will soon be able to be acquired at a much lower cost. Naturally, the incentive to return the shopping cart to a collection site will hardly still be there, and the deposit system will largely lose its purpose.
From this viewpoint, the object of the present invention is to improve upon the above-described deposit system, so that its misuse through lesser valued chips and the like is precluded. A solution first considered by the inventors to prevent the misuse of deposit locks was to install coin testers similar to those used in vending machines, which detect not only the diameter of the coin, for example, but also its weight, its thickness or the like. However, with this, the price of the deposit lock would be uneconomically high.